1. Field of the Invention
This invention relates to a thermal noise thermometer operating on the principle that the temperature of a resistor is related to the magnitude of the thermal noise signal (voltage, current, or power) produced in the resistor.
It is known in the art that a resistor at a temperature Tx produces a thermal noise signal caused by electron thermal motion. The effective value of this noise signal is expressed by the equation: EQU V = .sqroot.4K.multidot.Tx.multidot.Rx.multidot.B (1)
where K is Boltzmann's constant, Rx is the resistance of the resistor, and B is the frequency bandwidth of the thermal noise signal.
The present invention makes use of the relationship expressed by equation 1.
2. Description of the Prior Art
FIG. 1 is a block diagram of a conventional thermal noise thermometer in which the reference character Rx identifies a temperature detecting resistor placed at a temperature Tx to be measured, the reference character Rs identifies a standard resistor placed at a standard temperature Ts, the reference character A identifies an AC amplifier for amplifying thermal noise signals applied thereto through a switch S1, the reference character D identifies a rectifier for rectifying the output of the AC amplifier A, the reference characters H1 and H2 identify first and second hold circuits for holding signals fed thereto from the rectifier D through a switch S2 associated with the switch S1, and the reference legend COMP identifies a comparator for comparing the outputs of the first and second hold circuits H1 and H2.
The operation of the switches S1 and S2 in synchronism causes the comparator COMP to compare the magnitudes of the thermal noise signal V produced in the resistor R and the thermal noise signal Vs produced in the standard resistor Rs. Thus, while the switches S1 and S2 are operating, the operator can adjust the resistance of the resistor Rs such to equate the magnitudes of the thermal noise signals V and Vs. When the thermal noise signals V and Vs are equal in magnitude: EQU V = .sqroot.4K.multidot.Tx.multidot.Rx.multidot.B = Vs = .sqroot.4K.multidot.Ts.multidot.Rs.multidot.B (2)
the equation for the temperature Tx then can be written as: EQU Tx = Rs/Rx .multidot.Ts (3)
Thus, the temperature T can be calculated from the value of the resistance of the standard resistor Rs, the value of the resistance of the resistor Rx, and the value of the standard temperature Ts.
However, measurement of temperature by use of the above-described conventional method requires maintenance of the standard resistor at a standard temperature, for example, by placing the standard resistor in a thermostatically-controlled enclosure. This method also requires measurement of the value of the resistance of the resistor Rx.